Rain lake sim

Sardi Pax demonstrated rain “painting” a lake surface with drops, in Blender. The use of particle systems to dynamically paint surfaces has many applications in my sims. I’ve reproduced my attempt to simulate rain drops striking a mountain lake in this post, along with a few observations. I hope you enjoy it.

SP’s technique yielded a nice animation, but the still images I rendered were less clear. You can see the technique’s effect in this ‘Solid’ image:

The viewport raindrops in the above image are tinted red, and you can see the ‘spring’ force of a rain drop clearly in the lower right corner of the highlighted portion of the image.

I experimented in Blender to reduce the chaos caused by thousands of drops striking the water plane. I adjusted the ‘Damping,’ ‘Spring,’ and radii of influence of the various drops. When I duplicated the water plane to adjust these parameters, hiding the original, it crashed Blender. I theorized that removing an object with ‘key’ images initiated the crash in the animation section of Blender. Rather than duplicate the plane, I duplicated the material to adjust the nodes.

Restoring the object with key frames to the ‘Active’ seemed to eliminate the crash. I adjusted the animation in the ‘Graph Editor’ to allow linear interpolation. And, I disconnected the lower node circuit, at the ‘Math:Multiply’ node, albeit to little effect.

Too, I felt that my background image, the one I used as ‘Image as plane’ was brighter than SP’s source file. In the compositor, I ‘Color balanced’ the image, then filtered it in ‘Photos.’

I used an ‘Empty’ axis object as the focal point of the camera, placing it on the water plane in the middle of the scene. By adjusting the camera object ‘Size’ in the ‘Depth of Field’ panel, I defocused the fore- and background of the image, leaving the mid-section of the image, with the rain drops, sharp and clear.

Here is the image after I applied the ‘Photos:Instant’ filter.

A close-up of a drop immediately after it has struck the lake revealed that the technique yielded the desired result.

With the ‘Water’ plane as a dynamic paint ‘Canvas’ and the ‘Rain’ plane particle system designated as a dynamic paint ‘Brush,’ Sardi Pax provided a nice recipe for generating physics-based rain. Below is the layout of my scene, with annotations.

The following image is the same scene/file, with a different picture as the source for the backdrop. I’ve removed the defocus, but other than that minor adjustment, it is a simple swap of images. The difference is remarkable. Note the rain drop, and ‘spring’ effect near the base of the center tree. For these images, I disabled the camera’s ‘Motion blur’ effect, which is why we see a cartoon-shaped drop, as opposed to a spherical streak.

The above layout is based, of course, on SP’s clear and concise technique. I’ve included my Blender file here for review and testing.

Thanks for reading.

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